1. Field of the Invention
The present invention relates to a composition for forming an intermediate film, which is suitably used for the intermediate film for a laminated glass comprising ethylene vinyl acetate copolymer as a major component.
2. Description of the Related Art
A laminated glass having a structure that two sheets of glass are bonded through a transparent adhesive layer (intermediate film) is known. The use of the intermediate film enhances penetration resistance of the laminated glass. Even if the laminated glass for automobile is destroyed for the purpose of robbery or invasion, the window of the laminated glass cannot be opened. If external impact is given to the laminated glass, the transparent adhesive layer prevents the glass broken by the impact from scattering, because the layer adheres to pieces of the broken glass.
The laminated glass is used as a front glass and a side glass of airplane and vehicle, window glass of building, in addition to office automation equipment, office machinery and electronic device. Therefore, the laminated glass is required to have excellent transparency and appearance property, in addition to the penetration resistance and safety such as a prevention of scattering of broken glass.
However, the laminated glass has a problem that the appearance property and the transparency of it are reduced depending on use condition. Since a permeation of moisture and water at high temperature may form white spots in the intermediate film over time, the appearance property and the transparency of the laminated glass are reduced.
Polyvinyl butyral (hereinafter called “PVB”) is used for the intermediate film of laminated glass. However, the polyvinyl butyral which is thermoplastic resin is apt to be affected by the moisture. If an intermediate film comprising the polyvinyl butyral is left under high-humidity atmosphere for a long time, the transparent substrate is apt to detach from the intermediate film and white discoloration is apt to occur in the periphery of the intermediate film. As mentioned above, the water resistance of PVB is reduced. Therefore, Document 1 proposes a intermediate film which comprises an ethylene-vinyl acetate copolymer (hereinafter called “EVA”) having the excellent water resistance, and a laminated glass having a structure that two sheets of glass are bonded through the intermediate film.
The conventional intermediate film comprising EVA can be formed by subjecting a composition including EVA and a cross-linking agent to a molding process, for example by heat rolling using extrusion molding and the like. In addition, in order to enhance the gelation fraction and durability of EVA, cross-linking auxiliaries such as triallyl cyanurate and triallyl isocyanurate may be added to the composition to form the intermediate film (Document 2).    [Document 1] JP1982-196747 A    [Document 2] JP2005-001952 A